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**A rocket car is travelling at 648km/h[f] when the parachute is deployed and does 51.64MJ of work to slow the car down to a speed of 54.o km/h**

## Homework Equations

w = delta ek

w= m(1/2mvf^2 - 1/2mvi^2)

m= w/0.5(Vf^2-Vi^2)

## The Attempt at a Solution

i derived that equation from w=delta kinetic energy and i got 2/3 for showing work... this was a test question 4 months ago

now i have an exam tomorrow.

the mass i got is 248kg. the teacher took it up and the correct mass was 3210kg. i honestly feel my answer is correct and i constantly repeat this question and get 248 kg!!!

he said my formula is correct just the calculation is wrong:grumpy:

this is what i did.

51.64x10^6J/ -208494(negative since Vi > Vf so you get negative mass but i guess you ignore the negative)

can anyone tell me what i am doing wrong?!?!???!